Grid structure for cathode-ray tube

ABSTRACT

A grid structure or &#39;&#39;&#39;&#39;electron optical system&#39;&#39;&#39;&#39; formed integrally and used in a small-sized electron gun for focusing an electron beam generated in a cathode-ray tube, which grid structure comprises at least two disc-shaped apertured electrodes positioned closely adjacent to the cathode in parallel to each other and made of conductive or semiconductive materials such as metal or P-type and N-type semiconductive materials, respectively, and a disc-shaped barrier layer interposed fixedly between the two electrodes for electrically isolating the same from each other, whereby the electron beam passing through the aligned apertures is focused by the action of the potential difference established between the two electrodes.

United States Patent [72] lnventors Tomoyasu Nakano;

lkuo Matsuda; Jun Nlshida, all of Osaka,

Dec. 11, 1968, Japan, No. 43192494 [54] GRID STRUCTURE FOR CATHODE-RAYTUBE 19 Claims, 13 Drawing Figs.

[52] U.S. Cl 315/31, 313/64 [51] Int. Cl l-l0lj 29/56 [50] Field ofSearch 315/3 l;

3 l 3/64, 82 BF, 66, 352, 94

[5 6] Relerences Cited UNITED STATES PATENTS 3,250,920 5/1966 Wade315/94 Primary Examiner-Rodney D. Bennett, Jr. Assistant Examiner--N.Moskowitz Attorney-McCarthy, DePaoli, OBrien & Price ABSTRACT: A gridstructure or electron optical system" formed integrally and used in asmall-sized electron gun for focusing an electron beam generated in acathode-ray tube, which grid structure comprises at least twodisc-shaped apertured electrodes positioned closely adjacent to thecathode in parallel to each other and made of conductive orsemiconductive materials such as metal or P-type and N-typesemiconductive materials, respectively, and a disc-shaped barrier layerinterposed fixedly between the two electrodes for electrically isolatingthe same from each other, whereby the electron beam passing through thealigned apertures is focused by the action of the potential differenceestablished between the two electrodes.

PATENTEI) me! an 1629346 SHEET 1 BF 3 INVENTORS TOMOYASU NAKANO muoMATSUDA JUN NISHIDA' BY RCWML 'M.

ATTORNEYS mama nasal ran 33291646 (a) I (b) mvsmons TOMOYASU NAKANO IKUOMATSUDA JUN NISHIDA GRID STRUCTURE FOR CATI-IODE-RAY TUBE The presentinvention relates to improvement in an electron gun and in particular toa device or "electron optical system used in a small electron gun forfocusing an electron beam emitted from the cathode.

As is well known, numerous types of electron gun are used in cathode-raytubes. Where it is intended to fabricate a smallsized electron gun,however, there have been found difficulties in whatsoever type of theelectron gun. It is, for example, sometimes difficult to form aperturesin the grid and anode electrodes aligned with the cathode. Furthermore,it is almost impossible to accurately machine and assemble suchelectrodes, since they should be of a small size and be positioned at aclose spacing from each other and from the cathode.

It is, therefore, a primary object of the present invention to providean improved grid structure as applicable in a smallsized electron gun.

Another object of the invention is to provide a small grid structureformed integrally with proper alignment.

Still another object of the invention is to provide an improved deviceor electron optical system used in a small electron gun for focusing theelectron beam.

Other and further objects, advantages and features of the invention willbe apparent to those skilled in the art from the following description,taken in conjunction with the accompanying drawings, in which:

FIG. I is a lengthwise section of a cathode-ray tube equipped with aconventional electron gun but dispensing with usual deflection means;

FIG. 2a is a perspective view showing the grid structure according tothe present invention, which structure essentially corresponds to aportion of the electron gun shown in FIG. 1;

FIG. 2b is a section on line ll' of FIG. 2a;

FIG. 3a is a similar to FIG. 2a but shows a modification thereof;

FIG. 3b is a section on line IIII' of FIG. 30;

FIG. 4 is a block diagram of the electron gun equipped with the gridstructure shown in FIGS. 2a and 2b;

FIG. 5 is a similar to FIG. 4 but shows another grid structure shown inFIGS. 3a and 3b;

FIG. 6a is a block diagram showing a further modified grid structure;

FIG. 6b is similar to FIG. 6a but shows a still further modified gridstructure;

FIG. 7a is a lengthwise section of a still further modified gridstructure;

FIG. 7b is similar to FIG. 7a but shows a still further modified gridstructure;

FIG. 8a is a plan view of the grid structure as used in a colortelevision receiver of a shadow mask type; and FIG. 8b is a fragmentarysection on line IIIIII' of FIG. 8a.

Referring now to FIG. I, there is shown a typical cathoderay tube 10using a conventional electron gun with its deflection means removed. Theelectron gun, as shown on the lefthand side thereof, is equipped with aplurality of metal electrodes which are shown as divided into two groupsof A" and B" by their operations. One group A includes a cathode 11 anda first grid and second anode electrodes 12 and 13, respectively havingapertures located substantially centrally thereof. The group A," as awhole, acts not only as a generator of an electron beam but as focusingmeans providing a first beam focusing action, or crossover" action, asis often termed. The group B," on the other hand, includes a third,fourth, and fifth anode electrodes 14, 15 and 16, respectively, and assuch functions to focus secondly and accelerate the electron beam.

The operation of the group A" is such that the first grid electrode 12exercises a control over the amount of the electron beam to be emitted,while the second anode electrode 13 extracts or attracts the electronbeam from the cathode 11. This is because, in a conventional electrongun with a grounded cathode, the first grid electron 12 is usuallysupplied with a variable negative potential, whereas the second anodeelectrode 13 is maintained at a constant positive potential. In thismanner, the electron beam is controlled in its emission amount by thefirst grid electrode 12 and is extracted by the second anode electrode13.

Such control of the electron beam is, furthermore, considered ascribablenot only to the mask action of the apertures but also to the action ofrepulsion forces exerted because the electron beam and first gridelectrode 12 have the same polarity, i.e., the two are held at anegative potential. On the other hand, the crossover" action of thefirst beam focusing action is induced by the potential field establishedaxisymmetrically between the first grid and second anode electrodes 12and 13, respectively.

As will be discussed at greater length hereinafter, the presentinvention is directed to a small-sized grid structure fabricatedintegrally beforehand by interposing a barrier layer between the firstgrid and second anode electrodes, the three layers being held in contactwith each other.

In order to assist in understanding how the grid structure acts upon theelectron beam, reference will now be made to FIGS. 2a and 2b and FIGS.3a and 3b respectively showing a first and second embodiments of theinvention. For the sake of simplicity of explanation, the group A asshown in FIG. I will be assumed in the following figures to beessentially similar to the grid structures and therefore like referencenumerals are assigned to the parts corresponding to those in FIG. 1.

In FIGS. 2a and 2b, the grid structure comprises three concentricaldisc-shaped layers, i.e. a first grid electrode 17, insulator 18, andsecond anode electrode 19, each of which has formed centrally thereof asubstantially circular aperture of a suitable inside diameter. The firstgrid electrode 17 is disposed closely adjacent, in a face-to-facerelationship, to the cathode l1 and perpendicularly to the path of theelectron beam. These first and second electrodes 17 and 19,respectively, may be made of either conductive or semiconductivematerials. These material may be, for example, metal. The insulator orresistive layer 18 used as the barrier layer is tightly interposed orsandwiched between the two electrodes 17 and 19 in such a manner thatall these layers or, more precisely the central apertures therein, arein alignment. However, in a practical fabrication, the grid structure isformed integrally and is thereafter chemically etched at the centerthereof to form the aligned aperture of a suitable diameter.

In operation, a suitable voltage is applied from a DC voltage supply 20across the first grid and second anode electrodes 17 and 19 so that ahigh potential field is established in the internal space in theaperture. As a result, there are developed symmetrically of the barrierlayer 18 a plurality of electric lines of force 21, which act to bendinwardly or to focus the emitted electron beam, causing the crossoveraction. Thus, the grid structure A" acts as such an electron beamfocusing device as used in a small electron gun.

Turning to FIGS. 3a and 3b, a first grid electrode 17 is made of aP-type semiconductive material while a second anode electrode 19 is madeof an N-type semiconductive material. In this modification, the barrierlayer 18 is a depletion layer. Accordingly, these three layers 17, 18and 19 form a PN-junction as a whole with the two electrodes of oppositeconductivity type in electrical contact with each other.

In operation, when a reverse bias voltage is applied from a suitable DCvoltage supply 20 across the P- and N-type layers 17 and 19,respectively, and if the thickness of the depletion layer 18 is notnegligible over the dimensions of the apertures, then a potential fieldis established therein similarly to the former embodiment shown in FIGS.2a and 2b, thus producing the beam focusing action. Therefore, detaineddiscussion as to its operation may be herein omitted.

In FIG. 4, there is shown a practical circuit arrangement of an electrongun equipped with the grid structure A of the type shown in FIGS. 2a and2b. Across the grounded cathode 11 and first grid electrode 17 isapplied from a variable DC voltage' supply 22 a varying signal voltagewhich controls the amount of an electron beam 23 to be emitted inresponse to the applied signal. On the other hand, across the cathode IIand second anode electrode 19 is applied from a constant DC voltagesupply 24 a predetermined voltage which acts to extract from the cathode11 the electron beam 23. It, therefore, follows that the thus-controlledand focused electron beam 23 is accelerated by the remainingconventional anode electrodes 14, 15 and I6 and secondly focused into animage on the faceplate (not shown) of the cathode-ray tube.

Another modified grid structure is illustrated in FIG. 5. In thisinstance, across the first grid electrode 17 of P-type semiconductivematerial and the second anode electrode 19 of N-type semiconductivematerial is applied a varying signal voltage as a reverse bias voltageby a variable DC voltage supply 22, which controls the emission amountof the electron beam 23 in response to the applied signal. On the otherhand, between the grounded cathode II and the second anode electrode I9is supplied from a constant DC voltage supply 24 a predetermined voltagewhich holds the second electrode 19 at a positive potential and extractsfrom the cathode 11 the electron beam controlled by the first electrode17.

Here, if the cathode is grounded as usual, it is sufficient that thefirst grid and second anode electrodes 17 and !9 should be held atnegative and positive potentials, respectively. Hence, a number ofvariations thereof are conceivable without departing from theabove-described principle insofar as the electrical connections areconcerned.

In general, the control accuracy of the electron beam in cathode-raytubes depends mostly on the flying distance of the electron beam as wellas on the velocity thereof determined by the potential applied to theanode electrodes. As is well known, the depletion layer of a PN-junctionis inherently limited in its thickness. If, therefore, it is desired tomake the electron beam fly longer than the thickness of the depletionlayer under the focusing influence, the barrier layer may be madethicker if a PIN- or PNPN-junction of the PN-junction as described inconjunction with FIGS. 3a, 3b and 5.

Such modified examples are illustrated in FIGS. 6a and 6b. As shown inFIG. 6a, where a PIN-junction is used, to the grounded barrier layer oran intrinsic layer 18 is connected the positive terminal of the variableDC voltage supply 22. The first grid electrode 17 of a P-typesemiconductive material is connected to the negative terminal thereof,thus being maintained at a negative potential varying in response to thesignal applied thereto. Across the intrinsic layer 18 and second anodeelectrode 19 of an N-type semiconductive material is impressed by theconstant DC voltage supply 24 a predetermined voltage which holds thesecond electrode 19 positive. If, on the other hand, PNPN-junction is tobe used as shown in FIG. 6b, the barrier layer corresponds to anotherinternal PN- junction I8 and the N-type and P-type layers thereof aremaintained at the same potential of the ground as the cathode II. Theother electrical connections are similar to the case where aPIN-junction is used.

Still other modifications of the invention are shown in FIGS. 70 and 7b,wherein a highly resistive layer 25 with a circular aperture locatedsubstantially centrally thereof is fixedly interposed between thecathode and first grid electrode 17. In other words, the resistive layer25 is mounted securely on the first electrode 17 at the opposite side ofthe barrier layer 18. In this manner, the grid structure according tothe invention can be fabricated integrally with the cathode 11 so thatmore precise and easy gun alignment can be achieved. In FIG. 7b, thegrid structure is comprised by a PN-junction. The arrangement of thehighly resistive layer 25 is similar to that described in reference toFIG. 7a. It will be readily understood that this modification isapplicable to cases where PIN- or PNPN-junction is used in the gridstructure. Thus, the grid structure integrated with the cathode offerssatisfactory accuracy in assembly and proper gun alignment.

The grid structure according to the invention also finds wideapplications in practical multigun tubes, for example, for colortelevision receivers of a shadow mask type, as illustrated in FIG. 8. Inthis instance, the grid structure is assumed to be of the type ofPIN-junction by way of example only. The letters R, G and B assigned tothe grid structures are representative of the three elementary colors,i.e., red, green and blue used in a color television. The gridstructures R, G and B are shown as mounted on a common substrate 26,which corresponds to N- type semiconductive material and is disposed, ifdesired, at the vertexes of an equilateral triangle of suitabledimensions.

In a practical fabrication of such grid structures, intrinsic layers arefirst produced, for example, by diffusion method" at predeterminedpositions in the N-type substrate or the second anode electrode, onwhich are then produced by the similar method respective P-type layersor first grid electrodes. Upon completion of such processing, suitablecentral apertures are formed in the resultant layers for admitting theelectron beams representing the color signals, i.e., red, green andblue. With these arrangements, if variable signal voltages are appliedas reverse bias voltage across the common second electrode and therespective first electrodes, all of the grid structures R, G and B canbe controlled independently of one another.

As will be easily understood, the PIN-junction used in this modificationcan be replaced by all of the aforementioned embodiments. Wheresemiconductive materials such as PN- or PNPN-junction are employed forthe grid structures, similar method and arrangement may be employed forthe same purposes so that a detailed discussion may be omitted. However,where the grid structures are made of conductive materials as electrodesand of an insulator as a barrier layer, as described with reference toFIGS. 2a, 2b and 4, the common substrate should be made of any highlyresistive material, in which are embedded the respective gridstructures.

It will now be apparent from the foregoing description that thecombinations and arrangements of the grid structure as herein disclosedmay be varied without departing from the concept of the presentinvention. Thus, it will be understood that the embodiments of theinventive concept illustrated herein is exemplary and not limitative,since modifications and variations thereof, some of which have beenpointed out hereinabove, may be made without departing from the spiritand scope of the invention as claimed in the appended claims.

What is claimed is:

I. In a cathode-ray tube having a cathode, a grid structure for focusingan electron beam generated from said cathode comprising a first layer ofgrid electrode with a circular aperture formed substantially centrallytherein, which layer is disposed in a face-to-face relationship closelyadjacent to said cathode and perpendicularly to the path of said beamfor controlling the amount of the electron beam to be emitted inresponse to the variation in the electric potential applied thereto, asecond layer of anode electrode with a circular aperture formedsubstantially centrally therein, which layer is disposed closelyadjacent to and in alignment with said first electrode for extractingthe electron beam by the action of the electric potential appliedthereto, and a barrier layer with a circular aperture formedsubstantially centrally therein, which layer is interposed fixedlybetween said first and second layers for electrically isolating the samefrom each other, the apertures in said first, second and barrier layersbeing in alignment with one another and held in coaxial relationshipwith said cathode, whereby the electron beam passing through saidapertures is focused under the influence of the potential fieldestablished axisymmetrically within said apertures due to the difierencein the potentials applied to said two first and second layers.

2. A grid structure according to claim I, wherein said first and secondlayers are made of a conductive material and said barrier layer is madeof a highly resistive material.

3. A grid structure according to claim 2, wherein said conductivematerial is metal.

4. A grid structure according to claim 1, wherein said first and secondlayers are made of a semiconductive material and said barrier layer ismade of a highly resistive material.

5. A grid structure according to claim 4, wherein said first layer ismade of a P-type material, said second electrode is made of an N-typematerial and said barrier layer is a depletion layer, thereby forming aPN-junction as a whole by bringing said first and second layers ofopposite conductivity type into electrical contact.

6. A grid structure according to claim 4, wherein said first layer ismade of a P-type material, said second layer is made of an N-typematerial and said barrier layer is an intrinsic layer, thereby forming aPIN-junction as a whole by bringing said first and second layers ofopposite conductivity type into electrical contact.

7. A grid structure according to claim 4, wherein said first layer ismade of a P-type material, said second layer is made of an N-typematerial and said barrier layer is constituted generally of aPN-junction N-type layer of which is made contact with said first layerand P-type layer of which is made contact with said second layer,thereby forming a PNPN-junction as a whole by bringing said first andsecond layers of opposite conductivity type into electrical contact.

8. A grid structure according to claim 2, further comprising a highlyresistive layer with a circular aperture formed substantially centrallytherein, which resistive layer is fixedly interposed between saidcathode and said first layer for electrically isolating said cathode andsaid first layer from each other in such a manner that the apertures inall of said layers are in alignment with each other and held in coaxialrelationship with said cathode.

9. A grid structure according to claim 4, further comprising a highlyresistive layer with a circular aperture formed substantially centrallytherein, which resistive layer is fixedly interposed between saidcathode and said first layer of semiconductive material for electricallyisolating said cathode and said first layer from each other in such amanner that the apertures in all of said layers are in alignment witheach other and held in coaxial relationship with said cathode.

10. A multigun tube comprising at least two of said grid structuresaccording to claim 2, which grid structures are embedded in a commonsubstrate made of a highly resistive material, wherein the electronbeams emitted from the respective cathodes and admitted through therespective apertures are focused independently of one another.

ll. A multigun tube according to claim 10, wherein said multigun tube isof shadow mask type and is used for a color television receiver withsaid grid structures positioned at the vertexes of an equilateraltriangle.

12. A multigun tube comprising at least two of said grid structuresaccording to claim 4, which grid structures are embedded in a commonsubstrate made of a highly resistive material, wherein the electronbeams emitted from the respective cathodes and admitted through therespective apertures are focused independently of one another.

13. A multigun tube according to claim 12, wherein said multigun tube isof shadow mask type and is used for a color television receiver withsaid grid structures positioned at the vertexes of an equilateraltriangle.

14. A multigun tube comprising at least two of said grid structuresaccording to claim 2, which grid structures have a common substrate madeof a conductive material on which are respectively mounted highlyresistive layers on which are further mounted respective conductivelayers, wherein the electron beams emitted from the respective cathodesand ad mitted through the respective apertures are focused independentlyof one another.

15. A multigun tube according to claim 14, wherein said multigun tube isof shadow mask type and is used for a color television receiver withsaid respective grid structures positioned at the vertexes of anequilateral triangle.

16. A multigun tube comprising at least two of said grid structuresaccording to claim 4, which grid structures have a common substrate madeof a semiconductive material on which are respectively produced barrierlayers on which are further produced respective semiconductive layers,wherein the electron beams emrtted from the respective cathodes andadmitted through the respective apertures are focused independently ofone another.

17. A multigun tube according to claim 16, wherein said multigun tube isof shadow mask type and is used for color television receivers with saidrespective grid structures positioned at the vertexes of an equilateraltriangle.

18. An electron beam focusing device comprising said grid structureaccording to claim 2, wherein a variable DC voltage is applied acrosssaid cathode and said first layer which is maintained at a varyingnegative potential and a constant DC voltage is applied across saidcathode and said second layer which is maintained at a predeterminedpositive potential.

19. An electron beam focusing device comprising said grid structureaccording to claim 4, wherein a variable DC voltage is applied acrosssaid cathode and said first layer which is maintained at a varyingnegative potential and a constant DC voltage is applied across saidcathode and said second layer which is maintained at a constant positivepotential.

1. In a cathode-ray tube having a cathode, a grid structure for focusingan electron beam generated from said cathode comprising a first layer ofgrid electrode with a circular aperture formed substantially centrallytherein, which layer is disposed in a face-to-face relationship closelyadjacent to said cathode and perpendicularly to the path of said beamfor controlling the amount of the electron beam to be emitted inresponse to the variation in the electric potential applied thereto, asecond layer of anode electrode with a circular aperture formedsubstantially centrally therein, which layer is disposed closelyadjacent to and in alignment with said first electrode for extractingthe electron beam by the action of the electric potential appliedthereto, and a barrier layer with a circular aperture formedsubstantially centrally therein, which layer is interposed fixedlybetween said first and second layers for electrically isolating the samefrom each other, the apertures in said first, second and barrier layersbeing in alignment with one another and held in coaxial relationshipwith said cathode, whereby the electron beam passing through saidapertures is focused under the influence of the potential fieldestablished axisymmetrically within said apertures due to the differencein the potentials applied to said two first and second layers.
 2. A gridstructure according to claim 1, wherein said first and second layers aremade of a conductive material and said barrier layer is made of a highlyresistive material.
 3. A grid structure according to claim 2, whereinsaid conductive material is metal.
 4. A grid structure according toclaim 1, wherein said first and second layers are made of asemiconductive material and said barrier layer is made of a highlyresistive material.
 5. A grid structure according to claim 4, whereinsaid first layer is made of a P-type material, said second electrode ismade of an N-type material and said barrier layer is a depletion layer,thereby forming a PN-junction as a whole by bringing said first andsecond layers of opposite conductivity type into electrical contact. 6.A grid structure according to claim 4, wherein said first layer is madeof a P-type material, said second layer is made of an N-type materialand said barrier layer is an intrinsic layer, thereby forming aPIN-junction as a whole by bringing said first and second layers ofopposite conductivity type into electrical contact.
 7. A grid structureaccording to claim 4, wherein said first layer is made of a P-typematerial, said second layer is made of an N-type material and saidbarrier layer is constituted generally of a PN-junction N-type layer ofwhich is made contact with said first layer and P-type layer of which ismade contact with said second layer, thereby forming a PNPN-junction asa whole by bringing said first and second layers of oppositeconductivity type into electrical contact.
 8. A grid structure accordingto claim 2, further comprising a highly resistive layer with a circularaperture formed substantially centrally therein, which rEsistive layeris fixedly interposed between said cathode and said first layer forelectrically isolating said cathode and said first layer from each otherin such a manner that the apertures in all of said layers are inalignment with each other and held in coaxial relationship with saidcathode.
 9. A grid structure according to claim 4, further comprising ahighly resistive layer with a circular aperture formed substantiallycentrally therein, which resistive layer is fixedly interposed betweensaid cathode and said first layer of semiconductive material forelectrically isolating said cathode and said first layer from each otherin such a manner that the apertures in all of said layers are inalignment with each other and held in coaxial relationship with saidcathode.
 10. A multigun tube comprising at least two of said gridstructures according to claim 2, which grid structures are embedded in acommon substrate made of a highly resistive material, wherein theelectron beams emitted from the respective cathodes and admitted throughthe respective apertures are focused independently of one another.
 11. Amultigun tube according to claim 10, wherein said multigun tube is ofshadow mask type and is used for a color television receiver with saidgrid structures positioned at the vertexes of an equilateral triangle.12. A multigun tube comprising at least two of said grid structuresaccording to claim 4, which grid structures are embedded in a commonsubstrate made of a highly resistive material, wherein the electronbeams emitted from the respective cathodes and admitted through therespective apertures are focused independently of one another.
 13. Amultigun tube according to claim 12, wherein said multigun tube is ofshadow mask type and is used for a color television receiver with saidgrid structures positioned at the vertexes of an equilateral triangle.14. A multigun tube comprising at least two of said grid structuresaccording to claim 2, which grid structures have a common substrate madeof a conductive material on which are respectively mounted highlyresistive layers on which are further mounted respective conductivelayers, wherein the electron beams emitted from the respective cathodesand admitted through the respective apertures are focused independentlyof one another.
 15. A multigun tube according to claim 14, wherein saidmultigun tube is of shadow mask type and is used for a color televisionreceiver with said respective grid structures positioned at the vertexesof an equilateral triangle.
 16. A multigun tube comprising at least twoof said grid structures according to claim 4, which grid structures havea common substrate made of a semiconductive material on which arerespectively produced barrier layers on which are further producedrespective semiconductive layers, wherein the electron beams emittedfrom the respective cathodes and admitted through the respectiveapertures are focused independently of one another.
 17. A multigun tubeaccording to claim 16, wherein said multigun tube is of shadow mask typeand is used for color television receivers with said respective gridstructures positioned at the vertexes of an equilateral triangle.
 18. Anelectron beam focusing device comprising said grid structure accordingto claim 2, wherein a variable DC voltage is applied across said cathodeand said first layer which is maintained at a varying negative potentialand a constant DC voltage is applied across said cathode and said secondlayer which is maintained at a predetermined positive potential.
 19. Anelectron beam focusing device comprising said grid structure accordingto claim 4, wherein a variable DC voltage is applied across said cathodeand said first layer which is maintained at a varying negative potentialand a constant DC voltage is applied across said cathode and said secondlayer which is maintained at a constant positive potential.